Alcator C-Mod: A high-field divertor tokamak

Abstract

The Alcator C-Mod tokamak is a new device presently under construction at Massachusetts Institute of Technology (M.I.T.) which is scheduled to begin operation in mid-1990. The projected operating parameters are as follows: Toroidal field of 9 T; I p ≤ 3 MA, R = 66.5 cm, a = 21 cm, κ ≤ 2.0, δ ≤ 0.5, n e ≤ 10 21 m −3, P ICRF ≤ 6 MW. The divertor configuration includes mechanical baffling as opposed to an ‘open’ geometry. Under strictly ohmic heating conditions, central T i and T e are predicted to be in the range 2.5–3.5 keV over the density range (4–8) × 10 20 m −3. With the addition of 6 MW of ICRF heating, T i should vary from 4–8 keV over the same density range (assuming either Kaye-Goldston or Neo-Alcator scalings for electron confinement). Based on edge plasma characterizations from Alcator-C and divertor tokamaks, the scrape-off layer (SOL) properties are predicted to be: λ n ≈ 10mm, density at the divertor plate < 2 × 10 21 m −3, H 0 ionization mean free path between 1 and 10 mm. Maximum heat loads on various internal components are predicted to be in the range 5–10 MW/m 2. The flexibility of the poloidal field system in forming a number of flux surface geometries will provide further comparisons of the relative impurity control capabilities of double-null, single-null and limiter plasmas.